Initially I just installed Ubuntu on another drive and made sure it was EFI bootable, then replaced it with the original drives.
Now I’m using an USB stick which brings up ssh server and went from there (debootstrap). Note that you need to keep the reset button pressed until it says loading into recovery.
But it should also be possible to create an USB stick that brings up the (text) installer accessible through ssh:
https://help.ubuntu.com/community/Installation/NetworkConsole
The boot however remains flicky, it has a tendency to get stuck somewhere 2 out of 3 boots.
